Resins having extremely low molecular weights are sometimes used in toners for high speed printers and copiers. Such ultra-low molecular weight resins are typically blended with resins of much higher molecular weights to provide desired characteristics. For instance, the ultra-low molecular weight resin in the blend provides for good fusion and flow characteristics at the temperatures encountered in the copier or printer. They also fuse and melt very quickly after being heated which is extremely important since in high speed operations, it is essential for them to fuse and flow very quickly. On the other hand, polymers having number average molecular weights of 200,000 to 300,000 are typically included in such blends to prevent the toner resin from being too sticky. In some cases, polymers of extremely low molecular weights and intermediate molecular weights and a high molecular weight are blended to make toners having the characteristics desired.
It is extremely difficult to make the ultra-low molecular weight polymers needed in such toner applications by standard emulsion polymerization techniques. The molecular weight of polymers produced by free radical emulsion polymerization decreases as the amount of initiator utilized in the polymerization is increased. However, as the amount of initiator used is increased to higher and higher levels, the resulting polymerization reaction becomes increasingly more difficult to control. The reaction also proceeds very rapidly at very high levels of initiator making temperature control very difficult. For these reasons, it is not practical to utilize an initiator level of greater than about 0.6 phm (parts per hundred parts by weight of monomer). Chain transfer agents can also be used to reduce the molecular weight of polymers made by free radical emulsion polymerization. However, the extent to which chain transfer agents can reduce the molecular weight of the polymer is limited. For instance, chain transfer agents typically result in a maximum molecular weight reduction when used at a level of about 2.5 phm. The use of higher levels of chain transfer agents typically does not result in further molecular weight reduction. Furthermore, the use of chain transfer agents in large amounts can lead to other problems, such as undesirable odors. For these reasons, toner resins having number average molecular weights of less than about 18,000 are virtually impossible to make by free radical emulsion polymerization.
It is known that carbon-to-carbon double bonds in organic compounds can be cleaved by ozonylsis. The reaction through which ozone cleaves the double bonds in organic compounds can be depicted as follows: ##STR1## In the absence of zinc, hydrogen peroxide is formed which may degrade the carbonyl products formed by oxidation. In such a scenario, the hydrogen peroxide reacts with the aldehydes produced by ozonylsis and converts them to carboxylic acids. A more detailed description of ozonolysis is provided by J. March, Advanced Organic Chemistry: Reactions, Mechanisms and Structure; pages 871-874 (McGraw-Hill Book Company, 1968) and by R. T. Morrison and R. N. Boyd, Organic Chemistry; Third Edition; pages 218-219 (Allyn and Bacon, Inc., 1973). U.S. Pat. No. 5,039,737 discloses that ozone can be used to reduce the level of residual hydrazine in latices.